1. Field of the Invention
The present invention generally relates to a viscous fluid type heat generator in which heat is generated by forcibly shearing a viscous fluid confined in a chamber and the heat is transmitted to a heat exchanging liquid circulating through a heating system. More particularly, the present invention relates to a viscous fluid type heat generator provided within an ability to quickly change a heat-generation performance in response to a change in a requirement for either increasing or reducing heating to be applied to an objective heated area.
2. Description of the Related Art
Japanese Unexamined (Kokai) Utility Model Publication No. 3-98107 (JU-A-3-98107) discloses a viscous fluid type heat generator adapted for being incorporated into an automobile heating system as a supplemental heat source. The viscous fluid type heat generator of JU-A-3-98107 is formed as a heat generator provided with a unit for changing a heat-generation performance. The heat generator of JU-A-3-98107 includes front and rear housings connected together to form a housing assembly in which a heat generating chamber for permitting a viscous fluid to generate heat, and a heat receiving chamber arranged adjacent to the heat generating chamber for receiving the heat from the heat generating chamber, are formed. The heat receiving chamber in the housing assembly permits a heat exchanging liquid to flow therethrough and to receive heat from the viscous fluid in the heating generating chamber. The heat exchanging liquid is circulated through the heat receiving chamber and a separate heating circuit of the automobile heating system so as to supply the heat to the objective area, e.g., a passenger compartment of the automobile during the operation of the heating system. Thus, the housing assembly of the heat generator has an inlet port and an outlet port through which the heat exchanging liquid flows into and out of the heat receiving chamber. The heat generator of JU-A-3-98107 further includes a drive shaft rotatably supported by bearings which are seated in the front and rear housings of the housing assembly. A rotor element is mounted on the drive shaft so as to be rotated together with the drive shaft within the heat generating chamber. The inner wall surface of the heat generating chamber and the outer surfaces of the rotor element define labyrinth grooves in which the viscous fluid such as silicone oil having a chain-molecular structure is held to generate heat, in response to the rotation of the rotor element.
The heat generator of JU-A-3-98107 has such a characteristic arrangement that upper and lower housings are attached to a bottom portion of the housing assembly to form a heat generation control chamber therein. The heat generation control chamber is formed as a volume-variable chamber having a wall consisting of a membrane such as a diaphragm.
The heat generating chamber communicates with the atmosphere via a through-hole bored in an upper portion of the front and rear housings of the housing assembly, and with the heat generation control chamber via a communicating channel arranged between the heat generation control chamber and the heat generating chamber. The volume of the heat generation control chamber is adjustably changed by the movement of the diaphragm which is caused by a spring element having a predetermined spring factor or an externally supplied signal such as a pressure signal supplied from an engine manifold of an automobile.
When the drive shaft of the heat generator of JU-A-3-98107 incorporated in an automobile heating system is driven by an automobile engine, the rotor element is rotated within the heat generating chamber, so that heat is generated by the viscous fluid to which a shearing force is applied between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. The heat generated by the viscous fluid is transmitted from the heat generating chamber to water circulating through the heating system and carried by the water to a heating circuit of the heating system to warm an objective heated area such as a passenger compartment.
When it is detected that the objective area is excessively heated with respect to a reference temperature value predetermined for that area, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved in response to a vacuum pressure signal supplied from the engine manifold to increase the volume of the heat generation control chamber. Accordingly, the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber to reduce generation of heat by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. Therefore, the heat generating performance can be reduced, i.e., application of heat to the objective heated area becomes weak.
When it is detected that heating of the objective heated area is excessively weak with respect to the predetermined reference temperature value, through the detection of the temperature of the viscous fluid, the diaphragm of the heat generation control chamber is moved by the pressure signal and by the spring force of the spring element to reduce the volume of the heat generation control chamber. Therefore, the viscous fluid contained in the heat generation control chamber is supplied into the heat generating chamber so as to increase heat generation by the viscous fluid between the inner wall surface of the heat generating chamber and the outer surfaces of the rotor element. As a result, the heat generating performance can be increased, i.e., application of heat to the objective heated area becomes strong.
Nevertheless, in the variable heat generating performance, viscous fluid type heat generator of JU-A-3-98107, when the viscous fluid is withdrawn from the heat generating chamber into the heat generation control chamber, the atmospheric air is introduced from the through-hole of the housing assembly into the heat generating chamber so as to remove a vacuum occurring in the heat generating chamber due to the withdrawal of the viscous fluid therefrom. Thus, the viscous fluid must come into contact with the atmospheric air many times when the change of the heat generating performance occurs, and is oxidized. Therefore, a gradual degradation of the heat generating characteristics of the viscous fluid occurs. Further, the above-mentioned through-hole formed in the housing assembly permits a certain amount of moisture to enter from the atmosphere into the heat generating chamber of the heat generator, and accordingly, the viscous fluid is adversely affected by the moisture within the heat generating chamber after a long operation time of the heat generator, so that the heat generating characteristics of the viscous fluid must be again degraded.
The copending Japanese Patent Application No. 7-285266 discloses a different viscous fluid type heat generator having a variable heat-generating performance, in which a heat generating chamber defined in a housing assembly is fluid-tightly sealed and, a rotor element is rotated within the fluid-tight heat generating chamber to apply a shearing force to a viscous fluid held in gaps between the inner wall surface of the heat generating chamber and outer surfaces of the rotor element. Therefore, the viscous fluid in the heat generating chamber does not come into contact with the air and the moisture in the atmosphere and accordingly, the viscous fluid is degraded by neither the air nor the moisture. Therefore, the heat generator of the copending Japanese Patent Application No. 7-285266 is improved over that of JU-A-3-98107. Nevertheless, the variable heat-generating performance type heat generator of the copending Japanese Patent Application No. 7-285266 must still suffer from an unsatisfactory performance from the viewpoint of a quickly responding function in changing the heat-generating performance from a high to low performance when a heated area is excessively heated, and from a low to high performance when the heated area needs to be heated.
The viscous fluid type heat generator of the copending Japanese Patent Application No. 7-285266 includes a fluid-tight heat generating chamber in which a rotor element can be rotated to apply a shearing force to the heat-generating viscous fluid, a heat receiving chamber through which a heat exchanging liquid circulates to receive heat from the heat generating chamber, a heat generation control chamber capable of communicating with the heat generating chamber via a fluid withdrawing passage and via a fluid supply passage, and a control valve unit movable to regulate opening and closing of the fluid withdrawing and fluid supplying passages depending on a change in the temperature of the viscous fluid.
Due to the above-mentioned construction of the heat generator, a regulated withdrawal of the viscous fluid from the fluid-tight heat generating chamber into the heat Generation control chamber, and a regulated supply of the viscous fluid from the heat generation control chamber to the fluid-tight heat generating chamber can achieve a desired change in the heat generating performance of the heat generator.
The operation of the variable heat-generating performance, viscous fluid type heat generator of the copending Japanese Patent Application No. 7-285266 will be further described hereinbelow, with reference to FIGS. 5 through 7.
When it is required that the heat generator is able to quickly reduce the heat generating performance thereof at a given high temperature "A" (FIG. 5) of the viscous fluid, and to quickly increase the heat generating performance thereof at a given low temperature "B" (FIG. 5) of the viscous fluid, the control valve unit will be arranged, for example, so as to fully open the fluid withdrawing passage while simultaneously fully closing the fluid supplying passage when the temperature of the viscous fluid is at "A", and to fully close the withdrawing passage while simultaneously fully opening the fluid supplying passage when the temperature of the viscous fluid is at "B". However, as will be understood from FIG. 5, with the described arrangement of the control valve unit, it occurs that when the temperature of the viscous fluid approaches a given intermediate temperature "C" (FIG. 5) between the above high and low temperatures "A" and "B", the control valve unit is moved to its position where the unit closes the fluid withdrawing passage until the passage is brought to a state immediately before it is completely closed. Simultaneously, the control valve unit brings the fluid supplying passage to a state where it is opened slightly. At this moment, the viscous fluid in the heat generating chamber generates heat to cause a rise in a pressure thereof within the heat generating chamber. Thus, the viscous fluid is urged by the pressure to flow and leak from the heat generating chamber into the heat generation control chamber via the fluid withdrawing passage. On the other hand, since the fluid supplying passage is in a slightly (incompletely) opened position, and since a pressure rise within the heat generation control chamber is smaller than that in the heat generating chamber, a substantial supply of the viscous fluid from the heat generation control chamber into the heat generating chamber does not take place, and therefore, the heat generating performance of the heat generator is reduced while reducing a supply of heat from the heat generator to the heating system. As a result, the temperature of the viscous fluid is gradually lowered, and the rise in the pressure within the heat generating chamber is stopped to terminate leaking of the viscous fluid from the heat generating chamber into the heat generation control chamber. Further, when the temperature of the viscous fluid arrives at "C", and even if the fluid supply passage is widely opened by the control valve unit, the supplying of the viscous fluid from the heat generation control chamber to the heat generating chamber via the widely opened fluid supplying passage does not immediately take place because a fluid continuation, due to the viscosity, between the viscous fluid in the heat generation control chamber and that in the heat generating chamber through the fluid supply passage is broken when the fluid supplying passage approaches its closed condition. That is, the supply of the viscous fluid from the heat generation control chamber into the heat generating chamber starts with a given time of delay. When the temperature of the viscous fluid is further lowered from the temperature "C" of FIG. 5, the fluid withdrawing passage is completely closed and, the supply of the viscous fluid from the heat generation control chamber toward the heat generating chamber via the fluid supplying passage starts. Therefore, it is understood that in this heat generator, an increase in the heat generation performance cannot be achieved until the temperature of the viscous fluid drops to a temperature lower than the temperature "C". Accordingly, when the temperature of the viscous fluid is higher than "C" but appreciably lower than "A" in FIG. 5, even if an objective heated area demands to be quickly heated, the heat generator cannot quickly respond to such a demand. Namely, the response characteristics of the heat generator to the requirement for an increase in the heat generating performance is not satisfactory in a low temperature range of the viscous fluid, i.e., a low temperature range of the objective heated area.
On the other hand, when the heat generator is required to improve the characteristics thereof in response to a requirement for quickly increasing the heat generating performance of the heat generator when the temperature of the viscous fluid is at around an intermediate temperature "C", the control valve unit must be arranged so as to completely close the fluid withdrawing passage and simultaneously, to completely open the fluid supplying passage when the temperature of the viscous fluid arrives at "C" as shown in FIG. 6. Nevertheless, in the above-mentioned arrangement of the control valve unit, the fluid withdrawing passage is not sufficiently opened, and the fluid supplying passage is closed to a state immediately before it is completely closed when the temperature of the viscous fluid arrives at a given high temperature "A". Thus, the viscous fluid within the heat generating chamber cannot be smoothly withdrawn therefrom into the heat generation control chamber, and accordingly, a reduction in the heat generating performance thereof cannot be quickly achieved at the high temperature "A". Therefore, a response characteristics of the heat generator to a requirement for quickly reducing the heat generating performance in a high temperature range becomes worse to result in causing a thermal degradation of the viscous fluid.
Further, if the control valve unit of the abovementioned viscous fluid type heat generator of the copending Japanese Patent Application No. 7-285266 is arranged only so as to reduce the heat generating performance at a given high temperature of the viscous fluid, a bad response characteristics to a requirement for a quick increase in the heat generating performance must result as shown in FIG. 7. In FIG. 7, the temperature of the viscous fluid, i.e., a controlled variable, is replaced with the number of rotations of the drive shaft of the heat generator and shown in the abscissa, and the amount of heat generation by the viscous fluid is replaced with a torque, and shown in the ordinate. It will be understood from the graph of FIG. 7 that a curve illustrating a relationship between the number of rotations of the drive shaft and the torque demonstrates a hysteretic curve shown by a .fwdarw.b.fwdarw.c.fwdarw.a. This indicates that when the number of rotations of the drive shaft is reduced, and when a quick heating of an objective heated area is required, such requirement cannot be achieved quickly.